The invention relates to fluid delivery and recovery systems for the batch processing and cleaning with supercritical fluids, particularly to continuous flow, fluid delivery and recovery systems servicing a pressure vessel for supercritical phase cleaning and processing of semiconductor wafers as for removal of solvents, photo-resist materials, and loose particulate matter.
The use of supercritical fluids is well known in the literature, and a number of patents have been granted that include both delivery and recovery systems for the associated fluids. The use of supercritical fluids for treating various mechanical and electrical components is also well known in the literature. Published work refers to treating semiconductor wafers with supercritical fluids, with and without co-solvents or surfactants, to clean, strip solvents or photo-resist resins, dehydrate, or otherwise treat the wafers or structures on the wafers. In some cases, cycling pressure between high and low limits is practiced to achieve particular process performance. Such processes are necessarily batch operated; a sample or unit portion of the materials under process, such as a single semiconductor wafer, being sealed in a pressure vessel and processed to completion.
The extent to which these wafer treatments are successful in industrial practice depends in part on the ability to carry them out reliably and economically. Ideally, continuous flow, steady-state operation of a supercritical fluid-handling system is desirable for stable process control, but some processes require that some time be allocated at the beginning or end or some point in the middle of the operation for discontinuous or unsteady state flow functions such as heating, cooling, pumping to fill and empty vessels, and increasing or decreasing system pressures.
Semiconductor wafer processing in a manufacturing environment involves multiple batch operations with high cycling rates. The repetitive sequence of process operations may be automated by robot manipulation of wafers in enclosed xe2x80x9ccluster-toolsxe2x80x9d which interface to a number of process locations. Such automated systems require frequent loading and unloading of wafer process equipment, and require rapid cycling of pressures and temperatures in the process chambers if supercritical fluids are to be used.
Rapid cycling of fluid state or phase in a supercritical fluid process that involves, for example, rapid pressure changes, can lead to premature component failure due to the detrimental effects on seals, o-rings, and other wetted components made from polymers or elastomers. Extreme temperature changes associated with rapid pressure changes can cause valves and other components to freeze or fatigue, leading to unrecoverable system failure and costly downtime.
It is desirable, therefore, to provide a supercritical fluid delivery and recovery system that can operate at continuous flow, steady-state conditions, but can provide fluid to, and receive fluid and process byproducts from, a repetitive batch operation process that requires high-cycling and highly variable process conditions. It is also desirable to provide for automation of the fluid supply and recovery system and process chamber as in an automated wafer-factory as described above.
The invention, simply stated, is a continuous flow, steady state fluid delivery and recovery system for a process chamber requiring supercritical fluid and desired additives including co-solvents, for conducting repetitive batch processing operations in an automated environment. The delivery and recovery system provides for steady-state operation of fluid flow and byproducts recovery while the process chamber is brought rapidly and repeatedly on and off line, as in a production line operation where articles under process are sequentially loaded, subjected to a process that includes one or more supercritical phase steps, and unloaded for the next batch of materials under process.
It is an objective of the invention to provide embodiments that can be used with carbon dioxide, but the invention can be applied equally well with other gases. It is a further objective to provide for the ability to connect or isolate the process chamber at inlets and outlets with an automated valve system for rapid filling, exchanging, and purging of process fluids, with the capability of rapid cycling of pressure for rapid compression and/or decompression effects on the materials under process. It is another objective to provide a heating and cooling capacity that can be quickly applied to the process chamber for relatively fast temperature changes and tight temperature control of the process environment during repetitive batch processing operations, while providing for continuous flow, steady state operation of the fluid supply and recovery system.
It is yet another objective to provide the system elements necessary to operate in an automated mode for extended periods of operation, enabling repetitive process cycles to be completed as in production line fashion without operator intervention. It is still another objective to enable the system and chamber combination to be part of a larger manufacturing system or operation for processing semiconductor wafers.
It is an additional objective to provide a means for feeding the process chamber with process fluid, selectively with or without an additive such as a co-solvent, being already at the desired temperature and pressure, including at supercritical phase where desirable, without a delay period for purging the additive from intermediate devices, during repetitive batch processing operations, while providing for continuous flow, steady state operation of the fluid supply and recovery system.
It is a still additional objective of the invention to provide process chamber inlet and outlet fluid pressurization and flow capabilities sufficient for applying very rapid compression or decompression as intra-phase or inter-phase events to the materials under process within the chamber during repetitive batch processing operations, while providing for continuous flow, steady state operation of the fluid supply and recovery system. Intra-phase pressure and/or temperature changes would, for example, retain the process chamber fluids in the present phase, such as in supercritical phase; whereas inter-phase changes might move the fluids from supercritical phase to gas phase, or gas to liquid phase or state.
The invention includes a process fluid supply system, generally stored initially as a gas, and a supply system for co-solvent and/or surfactant for the process fluid, referred to as co-solvent. It includes a means to condense a process gas to a liquid, and a system to pump the condensed gas and co-solvent at high-pressure, mix them together, and heat them to supercritical state for delivery to a process chamber, or series of chambers. It may include one or more ballast tanks to provide a pressurized volume of the process-ready fluid mixture for applying rapid compression effects to the process chamber at supercritical phase or lower pressure levels. It may include special provisions for outflow capacity from the process chamber for applying rapid decompression effects to the chamber at supercritical phase or lower pressure levels. A bypass line with isolation valves allows for conducting a process cycle in the process chamber, including temperature and pressure ranging within the process chamber, independent of a steady state fluid circulation maintained within the supply and recovery system.
The gas supply system may include a bulk storage tank, filter, condenser, pressurized receiver tank, and delivery pump. The delivery pump can independently feed two or more supply lines to the chamber, one or more containing a process fluid and co-solvent mixture, and one with process fluid without co-solvent. The co-solvent supply system may include one or more bulk supply tanks, receivers, and delivery pumps.
The invention includes a recovery system to collect the process byproducts and purify the gas and liquid and return them to their respective receiver tanks, and a means to collect and remove process waste for appropriate disposition. The recovery system may consist of one or more flash separators to separate the gas from the liquid, a distiller/evaporator to re-distill the co-solvent, and a condenser to condense the co-solvent vapors to liquid.
The invention includes various pressure, temperature, and level transmitters, manual and automatic control valves, check valves, relief valves, rupture disks, and interconnecting piping and other hardware necessary to operate the process safely and effectively. The invention may be controlled by a digital controller in a control panel with appropriate user interface and display of information necessary for an operator to control and monitor the system.
The invention extends to and is inclusive of a gas supply system and separate supply systems for co-solvent and surfactant. It may include a means to condense the gas to a liquid, and a system to pump the condensed gas at high-pressure, mix it with co-solvent and surfactant in individual mixing tanks, and heat them to supercritical state for delivery through a ballast tank system or directly to a process chamber, or series of chambers. A bypass line with isolation valves allows repetitive batch operations of the process chamber independent of continuous fluid circulation in the supply and recovery system.
The gas supply system includes a bulk storage tank, filter, condenser, pressurized receiver tank, delivery pump, and discharge chamber. The delivery pump may independently feed three or more supply lines, leading to each of three or more ballast or discharge chambers. One discharge chamber may contain co-solvent, one may contain surfactant, and one may contain neither co-solvent nor surfactant. The co-solvent and surfactant supply systems may each include a bulk supply tank, receiver, and a delivery pump.
The invention services or may include one or more batch operated process chambers, and has the capacity to support, monitor and control internal chamber heaters or heat exchanger coils which have very rapid heating and cooling capacity, so as to provide full in-chamber process temperature control in addition to the pressure control provided by the fluid supply and recovery system.
The invention includes a recovery system to collect, separate and purify the byproduct gas, co-solvent, and surfactant and return them to their respective receiver tanks, and to collect and remove process waste for appropriate disposition. The recovery system may consist of a flash separator to separate the gas from the liquid, and two distiller/evaporators in series to re-distill the co-solvent and surfactant, and condensers to condense the co-solvent and surfactant vapors to liquid for return to their respective receivers.
A process chamber discharge receiver may be included to accept process chamber discharge during any rapid decompression steps which may occur during the process cycle. The receiver contents are vented into the recovery system for recycle.
The invention includes pressure, temperature, and level transmitters, manual and automatic control valves, check valves, relief valves, rupture disks, and interconnecting piping and other hardware necessary to operate the process safely and effectively. The invention may be controlled by a digital controller in a control panel with appropriate user interface and display of information necessary for an operator to interface with the system.
In summary, the invention combines broad temperature and pressure control of a batch operated supercritical process chamber, with full control of the associated, automated, continuous flow fluid supply and recovery control system, providing an integrated, full supercritical process operating system that can be integrated into a larger, automated, manufacturing system with front end and back end machinery and processes.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein we have shown and described only preferred embodiments of the invention, simply by way of illustration of the best mode contemplated by us on carrying out our invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.